Heretofore various types of cryogenic fuel tanks have been employed in an attempt to contain highly volatile fuels, such as Liquid Natural Gas, at acceptable pressure and with limited venting. In all cases the design emphasis has been placed on reducing the heat flow from the environment to the tank by well engineered thermal insulation. In the U.S. Pat. No. 2,795,937 a second fluid is cooled by the evaporating fuel during its use by an engine, the behaviour of the tank during storage periods being identical to that of any thermally insulated tank.
Since the heat flux from the environment to the fuel reserve cannot be completely eliminated, no matter how good the insulation, all existing designs of cryogenic fuel tanks present the undesirable features of venting or leaking part of the fuel and of uncontrollable variations of the fuel pressure in the tank which may present hazards or impair the proper performance of the engine. These disadvantages have been eliminated by the present invention which employs a secondary cryogenic liquid to absorb the heat flow from the surroundings, the secondary fluid being maintained at a lower temperature than that of the fuel by the aid of a refrigeration system operated between the secondary liquid and the fuel reserve.